1. Field of the Invention
The present invention relates to water-soluble polymers. More particularly, the present invention relates to novel water-soluble oxidation-reduction polymers having hydroquinone structures attached to the side chains of the polymers and to processes for producing the same.
2. Description of the Prior Art
Studies of polymers having oxidizing and reducing functions have been made with the objects of utilizing such polymers as an organic oxidant, a monomer stabilizer, an electron exchanger for a battery, or an agent for preparing hydrogen peroxide, removing oxygen contained in water, treating water or waste water in industry and the like. (See U.S. Pat. Nos. 2,992,899; 2,703,792 and 2,831,045; British Pat. Nos. 891,467 and 949,302; Ann. N.Y. Acad. Sci., 57 646 (1959) and Natl. Acad. Sci., U.S., 38 934 (1952).)
These oxidation-reduction polymers contain, as the functional group having oxidizing and reducing properties, hydroquinone groups, thiol groups, ketone groups, pyridine groups or ferrocene groups. Of these functional groups, however, hydroquinones are advantageous for a variety of reasons, e.g., excellent oxidation and reduction reversibility, appropriate oxidation-reduction potentials, stability and diversity of methods for their preparation, as described in large numbers of patents and literature references, e.g., U.S. Pat. Nos. 3,173,892 and 3,165,492; French Patent Nos. 1,362,707; 1,362,708 and 1,336,713; K. A. Kun and H. G. Cassidy, J. Polymer Sci., 44 383 (1960); ibid., 56 83 (1962); R. E. Moser et al., ibid., A2 2401 (1964); N. Nakabayashi, ibid., A-1, 6 869 (1968); G. Wegner, N. Nakabayashi and H. G. Cassidy, J. Org. Chem., 32 3155 (1967); G. Wegner et al., J. Polymer Sci., A-1, 6 3155 (1968); H. Kamogawa, ibid., B-3, 283 (1965); K. A. Kun et al., ibid., A3 1833 (1965); ibid., 4A-1, 847 and 859 (1966), etc.
These known polymers, however, are insoluble or poorly soluble in water and have only small oxidizing and reducing capacities as described, e.g., in H. G. Cassidy and K. A. Kun, Oxidation-Reduction Polymers, Interscience, New York (1965). In addition, their preparations are highly complicated.
U.S. Pat. No. 2,816,028 discloses polymers, which contain hydroquinone derivatives in their side chains, of the general formula: ##STR3## wherein R represents ##STR4## A represents a hydrogen atom, an alkyl group or a halogen atom; B represents a hydrogen atom or an alkyl group; Z represents --O-- or --NH--; x and y each represents a positive integer of 50 to 2,000; and n represents a positive integer of 1 to 6.
The above-described polymers are, however, water-insoluble except for those polymers where R is ##STR5## and hence possess only small oxidation-reduction capacities. The polymers in which R is ##STR6## are prepared using, as a starting material, poly(acrylic or methacrylic anhydride), which are obtained by polymerizing acrylic or methacrylic anhydride. However, it is extremely difficult to obtain soluble poly(acrylic or methacrylic anhydride), because the polymerization reaction of acrylic or methacrylic anhydride, each of which contains two double bonds having identical reactivity, is inevitably accompanied by a cross-linking reaction which results in the formation of insoluble gels. Moreover, the above-described polymers are not useful as an additive for photographic materials. This is thought to be due to the reduced oxidizing and reducing properties as a result of the electron-attracting carbonyl groups attached directly to the hydroquinone nuclei of the polymers.